The invention relates to a device for lubricating a rotary piston air pump. The pump is the type which is driven by an engine which is penetrated by lubricating oil return conduits. The device includes a rotary housing which is composed of a casing and two side walls and is rotatably mounted on a stationary axial having an eccentric thereon. The axle penetrates the housing perpendicularly with respect to the side walls and receives on its eccentric a rotating piston which is in camming engagement with the casing on limits volume changing operating chambers. The surface or mounting face of the eccentric on which the piston is positioned is provided with a recess communicating with a suction conduit and a recess communicating with a discharge conduit. Control openings in the piston communicate to these recesses successively with the operating chambers during the rotary movement.
German Petty Pat. No. 71 26 734 discloses a rotary piston air pump wherein the piston and/or the casing consists of a plastic material with a low friction value or is provided with self lubricating characteristics for reducing the friction generated within the pump. With such a measure the sliding characteristics may be improved, the wear reduced and the life span of the pump increased, but the problem of the generally insufficient sealing between the piston and the inner walls of the case cannot be eliminated, which results in an insufficient pump output, particularly at a lower speed.